Lincoln's victory in the election of 1864 was a. supported by northern soldiers furloughed home to support mcclellan at the polls. b. in doubt until the great union victories in the battles of atlanta and mobile bay. c. assured by popular support of the emancipation proclamation. d. due largely to the support of copperheads.

The correct answer is b: in doubt until the great Union victories in the Battles of Atlanta and Mobile Bay

Explanation:

President Lincoln (1809-1865) was re-elected in the Election of 1864 mostly because of the great Union victories in the Battles of Atlanta and Mobile Bay. These two were significant blows to the Confederacy, and until those victories, Lincoln winning the election had been much in doubt. One of the reasons was that the Civil War was taking longer than expected to come to an end - but the spirit and morale in the North were lifted due to the Union victory in the two battles. This was a crucial aspect that secured the re-election of President Lincoln, who, on November 8, defeated George McClellan (1826-1885), his Democratic competitor, once a Union general.

This 1864 presidential election was only held only for those states which had not separated themselves from the Union.